1. Technical Field
The present invention relates to a solenoid valve mounted to a shock absorber of a vehicle to adjust damping force.
2. Description of the Related Art
As a vehicle becomes popularized, a level of the customer's knowledge and requirement for the vehicle gets higher, and functional performances such as output power, silence, ride comfort, handling stability and the like as well as purpose, convenience and economical efficiency of the vehicle become import selection criterions of customers who will purchase a vehicle.
A vehicle is continuously subjected to vibration or shock transmitted from the road through road wheels during driving of the vehicle. Thus, a shock absorbing device is provided between a vehicle body (or a frame) and an axle (or a wheel shaft) to prevent vibration or shock from being transmitted directly to the vehicle body, thereby improving ride comfort of the vehicle. In addition, driving stability of the vehicle is improved by suppressing irregular vibration of the vehicle body. A suspension means a coupling device, including the aforementioned shock absorbing device, between a vehicle body and an axle. In general, the suspension comprises various components, such as chassis springs, shock absorbers for suppressing free vibration of the chassis spring to enhance ride comfort, a stabilizer for adjusting a vehicle height, a rubber bushing, a control arm and the like.
In particular, a shock absorber is mounted between a vehicle body (or a frame) and a road wheel in order to serve to suppress and damp the vibration transmitted from the road. The shock absorber absorbs vertical vibration energy of the vehicle body to enhance ride comfort, protect vehicle freight, and reduce dynamic stress of each part of the vehicle body, thereby increasing durability/lifespan of the vehicle. In addition, the shock absorber suppresses movement of an unsprung mass to secure ground contact performance of a tire and suppresses a change of attitude of the vehicle caused by inertial force, thereby enhancing dynamic performance of the vehicle.
In the meantime, in order to enhance ride comfort or handling stability of the vehicle according to a road condition and driving state, a damping force variable shock absorber capable of appropriately adjusting a damping force characteristic has been developed. In general, the conventional damping force variable shock absorber controls mainly a change of damping force in a solenoid operating manner and is generally classified into a reverse type and a normal type depending on a damping force control manner.
In particular, a normal type damping force variable shock absorber is configured such that rebound damping force and compression damping force are simultaneously increased or reduced according to solenoid current. For example, a conventional normal type damping force variable shock absorber controls the damping force in the rebound and compression strokes in a soft mode by applying predetermined solenoid current and controls the damping forces in the rebound and compression strokes in a hard mode by applying solenoid current higher than the predetermined value. The damping force control is achieved in such a manner that a spool moving according to operation of a solenoid controls the generation and adjustment of back pressure in a back pressure chamber (or a pilot chamber) formed in the rear of a disc valve for varying the damping force.
However, the disc valve for varying damping force of the aforementioned conventional shock absorber comprises a plurality of discs, a ring, a retainer and the like having various sizes and shapes, so that a structure of the disc valve is complicated. In addition, there are a large number of parts of the disc valve, so that the time and effort is enormously consumed in assembling the disc valve.